Research Report 2010 2011 - Helmholtz-Zentrum für ...

78 SCIENTIFIC REPORTS | Infection and Immunity | Microbial Pathogenesis
01.10 Molecular Mechanisms of Host-cell Pathogen
Interactions
PROJECT LEADER | Prof. Dr. Klemens Rottner | Former Research Group Cytoskeleton Dynamics |
krottner@uni-bonn.de
PROJECT MEMBERS | Dr. Jennifer Block | Dr. Stefan Köstler | Markus Ladwein | Margit Oelkers |
Dr. Malgorzata Szczodrak
This project aims at characterising the precise molecular
mechanisms driving actin reorganisation during different
types of motility processes and the interaction of different
pathogens with their hosts.
Actin polymerisation is catalysed by protein complexes
enhancing actin filament nucleation, such as the Arp2/3-
complex or formins. Prominent important actin regulators
include activators of Arp2/3-complex, e.g. WASP and
WAVE family members, which can operate downstream
of the Rho-GTPases Cdc42 and Rac1. Novel members of
this Arp2/3-complex activators include proteins of the
WHAMM/JMY subfamily and WASH (Rottner et al., 2010),
the latter of which we could recently identify to contribute
to Salmonella invasion (Hänisch et al., 2010).
Another prominent Arp2/3-complex binding protein that
had previously been implicated in dynamic actin reorganization
events such as lamellipodium protrusion or different
types of host-pathogen interaction is the Src-substrate
cortactin. We have generated cells and mice harbouring a
conditional mutation of the cortactin gene. To our surprise,
genetic removal of cortactin in fibroblasts did not abolish
Arp2/3-complex activation and actin polymerization
stimulated by constitutively active Rac1. However, cortactin
deletion abrogated signal transduction to activation of
Rac or Cdc42 small GTPases, for instance downstream of
growth factor activation, thus affecting migration and actin
reorganization more indirectly than previously thought (Lai
et al., 2009).
These results are consistent with more recent data obtained
by employing a novel actin assembly assay that we could
recently develop. We demonstrated that cortactin is incapable
of driving Arp2/3-complex-dependent actin assembly
at ectopic sites in living cytoplasm (Oelkers et al., submitted).
They also confirmed our previous data on the relative
turnover of cortactin and Arp2/3-complex in the lamellipodium,
which had already indicated that the majority of the
cortactin molecules associating with the structure cannot
engage in Arp2/3-complex activation at the lamellipodium
tip (Lai et al., 2008).
Fig. 1. Cortactin is essential for InlB-mediated Listeria invasion.
Quantification of Listeria entry in the presence (Control) and
absence (Cortactin KO) of cortactin, as indicated. Listeria
genetically deficient for both Internalin (A) and InlB (grey) were
used as non-specific invasion control. Graphic: HZI
Finally, in more recent efforts, we explored the role of
cortactin in different types of host-pathogen interaction.
Interestingly, cortactin appears essential for InlB-mediated
Listeria invasion (Fig. 1), but neither for entry triggered by
Shigella flexneri nor for actin pedestal formation induced
at the cell surface by different types of pathogenic E. coli
(Oelkers/Lai et al., unpublished).
Rottner, K., Hänisch, J., & Campellone, K. (2010) WASH, WHAMM and JMY: Regulation
of Arp2/3 complex and beyond. Trends in Cell Biology 20(11), 650-61.
Hänisch, J., Ehinger, J., Ladwein, M., Rohde, M., Derivery, E., Bosse, T., Steffen, A.,
Bumann, D., Misselwitz, B., Hardt, W.-D., Gautreau, A., Stradal, T.E.B., & Rottner, K.
(2010) Molecular dissection of Salmonella-induced membrane ruffling versus invasion.
Cellular Microbiology 12(1), 84-98.
Lai, F.P.L., Szczodrak, M., Oelkers, J.M., Ladwein, M., Acconcia, F., Benesch, S., Auinger,
S., Faix, J., Small, J.V., Polo, S., Stradal, T.E.B., & Rottner, K. (2009) Cortactin promotes
migration and platelet-derived growth factor-induced actin reorganization by signaling
to Rho-GTPases. Molecular Biology of the Cell 20(14), 3209-23.
Lai, F.P.L., Szczodrak, M., Block, J., Faix, J., Breitsprecher, D., Mannherz, H.G., Stradal,
T.E.B., Dunn, G.A., Small, J.V., & Rottner, K. (2008) Arp2/3-complex interactions and
actin network turnover in lamellipodia. EMBO Journal 27(7), 982-92.